Add structure to use test helpers.

This PR adds `routeFor` and `controllerFor` helpers.  

In using EAK in a project I found that I often repeat the `App.__container__.lookup('type:name');` setup stuff all over the place in my unit tests, and thought it may be useful to have a couple of small helpers for this. 

I also thought that it would be useful to have an established structure for how to include new test helpers.